TypeScript higher-order function for applying defaults to function with named parameters

index.ts

import { Diff } from 'typelevel-ts';

// Higher-order function
const withDefaultsFn = <DefaultParams extends object, Params extends DefaultParams, Result>(
    fn: (params: Params) => Result,
    defaultParams: DefaultParams,
) => (inputParams: Diff<Params, keyof DefaultParams>): Result =>
    fn({
        // We cast spreaded objects to any to workaround TS issue when spreading generic objects
        // https://github.com/Microsoft/TypeScript/issues/14409
        ...(defaultParams as any),
        ...(inputParams as any),
    });

function functionWithDefaultParams(a: string, b: number = 1) {}
functionWithDefaultParams('foo'); // defaults may be emitted
functionWithDefaultParams(); // non-defaults are required
functionWithDefaultParams(1); // non-defaults are type checked
functionWithDefaultParams('foo', 2); // defaults may be overridden

type Params = { a: string; b: number };
const defaults = {
    b: 1,
};
function functionWithParamsNamed(params: Params) {}
const functionWithDefaultParamsNamed = withDefaultsFn(functionWithParamsNamed, defaults);
functionWithDefaultParamsNamed({ a: 'foo' }); // defaults may be emitted
functionWithDefaultParamsNamed({}); // non-defaults are required
functionWithDefaultParamsNamed({ a: 1 }); // non-defaults are type checked
functionWithDefaultParamsNamed({ a: 'foo', b: 2 }); // defaults may be overridden

package.json

{
  "name": "with-defaults",
  "private": true,
  "scripts": {
    "lint": "tslint --project ./tsconfig.json",
    "compile": "tsc",
    "start": "npm run compile && npm run lint && node ./target/index.js",
    "format": "prettier --write './**/*.{ts,js,json}'"
  },
  "dependencies": {
    "typelevel-ts": "^0.3.1"
  },
  "devDependencies": {
    "prettier": "^1.13.5",
    "tslint": "^5.10.0",
    "tslint-language-service": "^0.9.9",
    "typescript": "^3.0.3"
  }
}

tsconfig.json

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es2015",
        "strict": true,
        "noImplicitReturns": true,
        "sourceMap": true,
        "outDir": "./target/",
        "rootDir": "./src/"
    },
    "files": ["./index.ts"]
}